What is anorectal melanoma?

Anorectal melanoma is a rare cancer that starts in the anus or rectum (back passage).

Anorectal melanoma is also called anorectal mucosal melanoma (ARMM).

Melanoma is a cancer that develops from cells called melanocytes, which give skin its colour. Melanoma usually starts in the skin. But there are also small numbers of melanocytes in the mucosa.

The mucosa is a tissue that lines various parts of the body including the anus and rectum. Melanoma that develops in the mucosa is called mucosal melanoma.

We have separate information about:

Symptoms of anorectal melanoma

The most common symptom is bleeding from the back passage (anus or rectum).

Other possible symptoms include:

  • pain or itching in the back passage
  • a lump in the back passage
  • a lump or swelling in the groin
  • a change in your bowel habits (diarrhoea, constipation or incontinence)
  • feeling like you need to poo, even though your bowel is empty.

Other conditions, such as haemorrhoids, can cause some of these symptoms. But if you have any of them, it is important to get them checked by your GP.

Causes of anorectal melanoma

We know that sun exposure is a risk factor for skin melanoma. But it is not a risk factor for anorectal melanoma. We do not know the causes of anorectal melanoma. It can happen at any age. But it is more likely to affect people over the age of 60.

Diagnosis of anorectal melanoma

You usually start by seeing your GP. They will feel your tummy (abdomen) and may examine your back passage. This is called a rectal examination.

Your GP will ask you to lie on your left side with your knees bent up towards your chest. They gently place a gloved finger with lubricating gel on it into your back passage to feel for any lumps or swelling. This may be uncomfortable, but it should not be painful. Tell them if it is painful.

Your GP will refer you to a hospital specialist if they are not sure what the problem is. They will also refer you if they think your symptoms may be caused by cancer.

At the hospital, the specialist doctor will ask you about your symptoms and general health. They will also examine you.

  • You will have another rectal examination.
  • Sometimes women may also have an internal examination of their vagina. This is because the vagina is very close to the anal canal. But this is usually done during surgery if you need it.
  • The doctor will also feel your groin to check for swollen lymph nodes. Lymph nodes are part of the body’s immune system which protects you from infection and disease.
  • The doctor will also arrange for you to have a biopsy – this is when the doctor removes a small piece of tissue to check it for cancer cells.

Waiting for tests results can be a difficult time, we have more information that can help.

Further tests

There are other tests that may be used to diagnose anorectal melanoma. These tests can also be used to check whether the cancer has spread. Tests may include:

  • CT scan

    A CT scan uses x-rays to build a 3D picture of the inside of the body.

  • MRI scan

    An MRI scan uses magnetism to build up a detailed picture of areas of your body.

  • PET-CT scan

    A PET-CT scan is a combination of a CT scan, which takes a series of x-rays to build up a 3D picture, and a positron emission tomography (PET) scan. A PET scan uses low-dose radiation to measure the activity of cells in different parts of the body.

  • Endorectal ultrasound scan (ERUS)

    An endorectal ultrasound scan (ERUS) uses sound waves to make up a picture of the anus and the rectum.

  • Ultrasound of the groin

    An ultrasound uses sound waves to make up a picture of an area of the body. You may have this test to look at the groin area.

  • Fine needle aspiration (FNA) of the lymph nodes

    You may have a fine needle aspiration (FNA) of the lymph nodes to check for cancer cells in the lymph nodes. The doctor puts a fine needle into the lymph node. They then withdraw a sample of cells into a syringe. The cells are sent to a laboratory to be checked for cancer.

  • Sentinel lymph node biopsy

    This test is not used often. You may have it if you are taking part in a clinical trial. It is used to check if the cancer has spread to the sentinel lymph nodes. These are the first lymph nodes that fluid drains to from anorectal melanoma. So if the anorectal melanoma has spread to nearby nodes, the sentinel nodes are most likely to be affected. We have more about sentinel lymph node biopsy in our skin melanoma information.

Staging of anorectal melanoma

The stage of a cancer describes its size and whether it has spread. Knowing the stage of the cancer helps doctors decide on the best treatment for you. We have more information about staging anorectal melanoma.

Treatment for anorectal melanoma

A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT).

Your doctor will explain the different treatments and their side effects. They will also talk to you about the things you should consider when making treatment decisions.

Your treatment plan will depend on several factors, including the stage of the cancer and your general health. Your doctor will talk to you about this. Together you can decide on the best treatment plan for you.

You may also have some treatments as part of a clinical trial.

Treatments for anorectal melanoma include:

  • Surgery

    The main treatment for anorectal melanoma is usually surgery.

  • Radiotherapy

    Radiotherapy uses high-energy rays to treat cancer. It destroys cancer cells in the area where it is given.

    If anorectal melanoma has spread to other areas of the body, you may have radiotherapy to control symptoms such as bleeding or pain.

  • Targeted therapy and immunotherapy

    Targeted therapy uses drugs to find and attack cancer cells. There are many different types of targeted therapy.

    Immunotherapy drugs use the body's immune system to find and attack cancer cells.

    There are several targeted therapy and immunotherapy drugs used to treat skin melanoma. These may be used for anorectal melanoma that has spread if surgery is not possible. 

After anorectal melanoma treatment

Follow-up

The aim of follow-up care is to make sure everything is going well and to find out if you have any concerns. You will have regular check ups. You may also have scans. Your doctor or nurse will tell you what to expect in your situation.

We have more information on follow-up care after treatment.

You may want to contact some other useful organisations:

  • Melanoma UK provides support and information for people with melanoma and their families.
  • Melanoma Focus commissions and funds melanoma research, and provides support and information for patients, carers and healthcare professionals.
  • Colostomy UK provides support and information for anyone who has, or is due to have, a colostomy.

Well-being and recovery

Even if you already have a healthy lifestyle, you may choose to make some positive lifestyle changes after treatment.

Making small changes such as eating well and keeping active can improve your health and wellbeing and help your body recover.

About our information


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Reviewed: 30 April 2020
Reviewed: 30/04/2020
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Next review: 30 April 2023
Next review: 30/04/2023